The addition of anticaking agents to single and binary blends of
deliquescent ingredients had variable effects on deliquescence behavior,
moisture sorption, and physical stability. Formulation, storage RH,
time, and RH cycling all significantly affected the physical stability of
the powder blends. In the majority of the host powders studied, calcium
stearate was the most effective anticaking agent at delaying the
onset of deliquescence, especially deliquescence lowering, decreasing
moisture sorption, and maintaining flowability over time at different
RHs. The addition of calcium silicate and silicon dioxide often reduced
the physical stability of the deliquescent host powders individually
and in blends, by increasing total moisture sorption above RH0 orRH0mix, decreasing RH0 or RH0mix, bringing water into the powdered
systems at RHs below the deliquescence point of the host powder,
and/or decreasing flowability and increasing caking. Temperature affected
caking to a lesser extent, with increasing temperatures typically
enhancing caking and decreasing RH0mix. Cycling the RH above and
below RH0 or RH0mix was the treatment that rendered the strongest
cakes, likely due to solid bridge formation between particles. A combination
of anticaking agents, one that can prevent contact between
two crystals and delay deliquescence during mixing and processing
operations, and one that will prevent solid bridges from forming
once the powder is stored at lower RHs, could better preserve the
physical integrity of powders and warrants further investigation.
These results indicate the importance of controlling the environmental
conditions and formulation strategies for maintaining or improving
the stability of crystalline deliquescent ingredients.